1. Field of Invention
The present invention relates generally to a semiconductor substrate processing system. More specifically, the invention relates to a method and apparatus for polishing a semiconductor substrate.
2. Description of the Background Art
In semiconductor substrate processing, the transfer of substrates between modules is required to optimize processing rates while minimizing risk of substrate damage and contamination. The typical method of transferring a substrate between processing and support equipment is to move the substrate using a paddle manipulated by a robot. In most instances, the substrate is lifted from a pedestal using pins to allow the paddle to be positioned under the center portion of the substrate. In other modules, such as transfer cassettes, the substrate is supported horizontally at the edges, allowing the paddle access under the substrate. The paddle is then lifted to engage the substrate and carry the substrate from one module or station to another. Often, the paddle is equipped with a mechanism that secures the substrate to the paddle during transfer and releases the substrate once the desired destination is reached. Such a mechanism may be a vacuum device, an electrostatic chuck, a substrate edge gripping mechanism and the like.
The traditional, horizontal paddle and retention mechanisms, while functional for passing substrates among certain semiconductor processing stages, are cumbersome when directed for use between certain other types of semiconductor processing stages. The transfer between a factory interface and a polisher on Chemical Mechanical Polishing (CMP) system is an example of an area where the horizontal orientation of the substrate during transfer is not efficient.
The polisher generally removes the surface roughness of a horizontally orientated substrate with the assistance of a slurry. After polishing the substrate, some of the slurry remains on the substrate. If the slurry dries and hardens on the substrate surface, the substrate may become damaged, defective or unfit for further processing. Therefore, the polished substrates are normally cleaned by spraying the substrates with a cleaning fluid, scrubbing the substrates, and by using megasonics. The substrates can be cleaned either in a horizontal or vertical position. Those substrates cleaned vertically benefit from the assistance of gravity in removing the slurry and other contaminants from the substrate.
The 90 degrees difference in substrate orientation between the polishing and cleaning processes leads to a number of problems for a system builder and operator when using a traditional horizontally orientated substrate transfer mechanism. One problem is that a larger machine foot-print is required to accommodate rinsing a substrate while the substrate is horizontal, added stations for orientating the substrates and/or increased transfer distances. Additionally, the extra steps in substrate handling increases the probability of costly substrate damage and contamination.
Therefore, there is a need in the art for apparatus which facilitates substrate transfer between modules of a semiconductor processing system, wherein vertical orientation of the substrate is used during substrate transfer.
One aspect of the present invention generally provides a system for polishing a substrate. Specifically, the system includes one or more polishing modules and a cleaning module. A rail is disposed between the polishing modules and the cleaning module. The rail has a first end disposed proximate a transfer station disposed on the polishing module and a second end disposed proximate the cleaning module. A robot is movably disposed on the rail. The robot is adapted to transfer a substrate between the transfer station and the cleaning module. Additional embodiments of the invention include having the cleaning module in an orientation perpendicular to an orientation of the rail and having the cleaning module in an orientation perpendicular to an orientation of the rail.